Rules registry

Where rule codes live, how they're organized, and how to look them up.

Source of truth

Single file: crates/ruff_linter/src/codes.rs. Every rule code (F401, B008, RUF019, etc.) is declared there with its rule struct and category. The schema generator and the docs site both read this mapping.

Categories

Rules are grouped by origin (Flake8 plugin name, Pylint, pyupgrade, isort, etc.) plus a few first-party Ruff families:

Prefix(es)	Source / family
F	Pyflakes
E, W	pycodestyle errors / warnings
C90	mccabe complexity
I	isort
N	pep8-naming
D	pydocstyle
UP	pyupgrade
YTT	flake8-2020
ANN	flake8-annotations
ASYNC	flake8-async
S	flake8-bandit
BLE	flake8-blind-except
FBT	flake8-boolean-trap
B	flake8-bugbear
A	flake8-builtins
COM	flake8-commas
CPY	flake8-copyright
C4	flake8-comprehensions
DTZ	flake8-datetimez
T10	flake8-debugger
DJ	flake8-django
EM	flake8-errmsg
EXE	flake8-executable
FA	flake8-future-annotations
ISC	flake8-implicit-str-concat
ICN	flake8-import-conventions
LOG	flake8-logging
G	flake8-logging-format
INP	flake8-no-pep420
PIE	flake8-pie
T20	flake8-print
PYI	flake8-pyi
PT	flake8-pytest-style
Q	flake8-quotes
RSE	flake8-raise
RET	flake8-return
SLF	flake8-self
SIM	flake8-simplify
SLOT	flake8-slots
TID	flake8-tidy-imports
TD, FIX	flake8-todos / flake8-fixme
TC	flake8-type-checking
ARG	flake8-unused-arguments
PTH	flake8-use-pathlib
TRY	tryceratops
FLY	flynt
NPY	NumPy-specific
AIR	Airflow-specific
PERF	Perflint
FURB	refurb
PD	pandas-vet
PGH	pygrep-hooks
PL, PLC, PLE, PLR, PLW	Pylint
RUF	First-party Ruff rules
FAST	FastAPI-specific

(Some less-common families omitted.)

Implementation locations

Each prefix maps to a directory under crates/ruff_linter/src/rules/<plugin>/. The plugin folder contains a rules/ subdirectory with one .rs file per rule. Snapshots and fixtures live alongside.

Selectors

Users select rules with code or category names:

• --select F enables all Pyflakes rules.
• --select F4 enables only the F4 group.
• --select F401 enables a single rule.
• --select ALL enables everything (rarely used in practice).
• --select EXTEND extends the existing set rather than replacing.

The selector grammar lives in crates/ruff_linter/src/rule_selector.rs.

Rule redirects

When a rule is renumbered or renamed, crates/ruff_linter/src/rule_redirects.rs keeps the old code resolvable so user configurations don't break. This is the only place where you'll ever see a "deprecated" code.

Rule explanations

Every rule has triple-slash documentation on its struct:

• What it does — one-paragraph summary.
• Why is this bad? — motivation.
• Example — minimal Python sample.
• Use instead — preferred alternative.
• Options — any rule-specific configuration.
• References — link to the upstream tool / PEP / issue.

These doc comments are rendered:

• On the docs site under Rules.
• By ruff rule <code> at the CLI.
• In editor hovers via the LSP.

ty diagnostics

ty's diagnostics are managed separately in crates/ty_python_semantic/src/lint.rs. They have short string ids (invalid-assignment, protocol-violation) instead of letter+number codes, and severity overrides via [lint] in the project config.

Where to look for "I just want to read all rules"

• crates/ruff_linter/src/codes.rs — the registry.
• crates/ruff_linter/src/rules/*/rules/*.rs — implementations and docs.
• docs/ — rendered docs (built by mkdocs from this metadata via cargo dev generate-all).